package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import org.apache.lucene.util.BitVector;
import org.apache.lucene.index.FieldInfo.IndexOptions;
import org.apache.lucene.store.IndexInput;

class SegmentTermDocs implements TermDocs {
    protected SegmentReader parent;
    protected IndexInput freqStream;
    protected int count;
    protected int df;
    protected BitVector deletedDocs;
    int doc = 0;
    int freq;

    private int skipInterval;
    private int maxSkipLevels;
    private DefaultSkipListReader skipListReader;

    private long freqBasePointer;
    private long proxBasePointer;

    private long skipPointer;
    private boolean haveSkipped;

    protected boolean currentFieldStoresPayloads;
    protected IndexOptions indexOptions;

    protected SegmentTermDocs(SegmentReader parent) {
        this.parent = parent;
        this.freqStream = (IndexInput) parent.core.freqStream.clone();
        synchronized (parent) {
            this.deletedDocs = parent.deletedDocs;
        }
        this.skipInterval = parent.core.getTermsReader().getSkipInterval();
        this.maxSkipLevels = parent.core.getTermsReader().getMaxSkipLevels();
    }

    public void seek(Term term) throws IOException {
        TermInfo ti = parent.core.getTermsReader().get(term);
        seek(ti, term);
    }

    public void seek(TermEnum termEnum) throws IOException {
        TermInfo ti;
        Term term;

        // use comparison of fieldinfos to verify that termEnum belongs to the same segment as this SegmentTermDocs
        if (termEnum instanceof SegmentTermEnum && ((SegmentTermEnum) termEnum).fieldInfos == parent.core.fieldInfos) { // optimized case
            SegmentTermEnum segmentTermEnum = ((SegmentTermEnum) termEnum);
            term = segmentTermEnum.term();
            ti = segmentTermEnum.termInfo();
        } else { // punt case
            term = termEnum.term();
            ti = parent.core.getTermsReader().get(term);
        }

        seek(ti, term);
    }

    void seek(TermInfo ti, Term term) throws IOException {
        count = 0;
        FieldInfo fi = parent.core.fieldInfos.fieldInfo(term.field);
        indexOptions = (fi != null) ? fi.indexOptions : IndexOptions.DOCS_AND_FREQS_AND_POSITIONS;
        currentFieldStoresPayloads = (fi != null) ? fi.storePayloads : false;
        if (ti == null) {
            df = 0;
        } else {
            df = ti.docFreq;
            doc = 0;
            freqBasePointer = ti.freqPointer;
            proxBasePointer = ti.proxPointer;
            skipPointer = freqBasePointer + ti.skipOffset;
            freqStream.seek(freqBasePointer);
            haveSkipped = false;
        }
    }

    public void close() throws IOException {
        freqStream.close();
        if (skipListReader != null)
            skipListReader.close();
    }

    public final int doc() {
        return doc;
    }

    public final int freq() {
        return freq;
    }

    protected void skippingDoc() throws IOException {
    }

    public boolean next() throws IOException {
        while (true) {
            if (count == df)
                return false;
            final int docCode = freqStream.readVInt();

            if (indexOptions == IndexOptions.DOCS_ONLY) {
                doc += docCode;
                freq = 1;
            } else {
                doc += docCode >>> 1; // shift off low bit
                if ((docCode & 1) != 0) // if low bit is set
                    freq = 1; // freq is one
                else
                    freq = freqStream.readVInt(); // else read freq
            }

            count++;

            if (deletedDocs == null || !deletedDocs.get(doc))
                break;
            skippingDoc();
        }
        return true;
    }

    /** Optimized implementation. */
    public int read(final int[] docs, final int[] freqs) throws IOException {
        final int length = docs.length;
        if (indexOptions == IndexOptions.DOCS_ONLY) {
            return readNoTf(docs, freqs, length);
        } else {
            int i = 0;
            while (i < length && count < df) {
                // manually inlined call to next() for speed
                final int docCode = freqStream.readVInt();
                doc += docCode >>> 1; // shift off low bit
                if ((docCode & 1) != 0) // if low bit is set
                    freq = 1; // freq is one
                else
                    freq = freqStream.readVInt(); // else read freq
                count++;

                if (deletedDocs == null || !deletedDocs.get(doc)) {
                    docs[i] = doc;
                    freqs[i] = freq;
                    ++i;
                }
            }
            return i;
        }
    }

    private final int readNoTf(final int[] docs, final int[] freqs, final int length) throws IOException {
        int i = 0;
        while (i < length && count < df) {
            // manually inlined call to next() for speed
            doc += freqStream.readVInt();
            count++;

            if (deletedDocs == null || !deletedDocs.get(doc)) {
                docs[i] = doc;
                // Hardware freq to 1 when term freqs were not
                // stored in the index
                freqs[i] = 1;
                ++i;
            }
        }
        return i;
    }

    /** Overridden by SegmentTermPositions to skip in prox stream. */
    protected void skipProx(long proxPointer, int payloadLength) throws IOException {
    }

    /** Optimized implementation. */
    public boolean skipTo(int target) throws IOException {
        if ((target - skipInterval) >= doc && df >= skipInterval) { // optimized case
            if (skipListReader == null)
                skipListReader = new DefaultSkipListReader((IndexInput) freqStream.clone(), maxSkipLevels, skipInterval); // lazily clone

            if (!haveSkipped) { // lazily initialize skip stream
                skipListReader.init(skipPointer, freqBasePointer, proxBasePointer, df, currentFieldStoresPayloads);
                haveSkipped = true;
            }

            int newCount = skipListReader.skipTo(target);
            if (newCount > count) {
                freqStream.seek(skipListReader.getFreqPointer());
                skipProx(skipListReader.getProxPointer(), skipListReader.getPayloadLength());

                doc = skipListReader.getDoc();
                count = newCount;
            }
        }

        // done skipping, now just scan
        do {
            if (!next())
                return false;
        } while (target > doc);
        return true;
    }
}
